more intro

diff --git a/posic/publications/c_defects_in_si.tex b/posic/publications/c_defects_in_si.tex
index 94438bcd5aff607a4211e692b1b7e8a0f0f35a85..d3a7ecae91a4a0fd3db6d90fb47d9a3dc936d02f 100644 (file)
--- a/posic/publications/c_defects_in_si.tex
+++ b/posic/publications/c_defects_in_si.tex
@@ -40,24 +40,36 @@ Calculations using classical potentials are put aside first principles density f
 \r
 % there should be a short motivation for the material system!\r
 Silicon carbide (SiC) has a number of remarkable physical and chemical properties.\r
-The wide band gap semiconductor (2.3 eV - 3.3 eV) exhibiting a high breakdown field, saturated electron drift velocity and thermal conductivity in conjunction with its unique thermal and mechanical stability as well as radiation hardness is a suitable material for high-temperature, high-frequency and high-power devices\cite{wesch96}, which are moreover deployable in harsh environments\cite{capano97}.\r
+The wide band gap semiconductor (2.3 eV - 3.3 eV) exhibiting a high breakdown field, saturated electron drift velocity and thermal conductivity in conjunction with its unique thermal and mechanical stability as well as radiation hardness is a suitable material for high-temperature, high-frequency and high-power devices\cite{wesch96,morkoc94}, which are moreover deployable in harsh and radiation-hard environments\cite{capano97}.\r
 % there are different polytpes with different properties and 3c-sic in special\r
 SiC, which forms fourfold coordinated covalent bonds, tends to crystallize into many different modifications, which solely differ in the one-dimensional stacking sequence of identical, close-packed SiC bilayers\cite{fischer90}.\r
 Different polytypes exhibit different properties, in which the cubic phase (3C-SiC) shows increased values for the thermal conductivity and breakdown field compared to other polytypes\cite{wesch96}, which is thus most effective for high-performance electronic devices.\r
 \r
 % (thin films of) 3c-sic can be produced by ibs\r
-Next to 3C-SiC epitaxial layer growth by chemical vapor deposition (CVD) on 6H-SiC substrates\cite{powell90} or molecular beam epitaxy on silicon\cite{} as well as 6H-SiC\cite{}, ion beam synthesis (IBS) constitutes a promising method to produce 3C-SiC epitaxial layers of high quality in crystalline silicon\cite{lindner02} (c-Si).\r
-Highly energetic carbon ions are ...\r
-\r
-The relevant structures are with $\approx$ 20000 atoms/nanocrystal way too large to be completely be described with high accuracy \r
-quantum mechanical methods. Modelling the processes described above require the use of less accurate methods, like e.g. classical \r
-potentials (Erhard/Albe\cite{albe},Stillinger-Weber\cite{stillinger},...).  Whether such potentials are appropriate for the description of the \r
-physical problem has, however, to be verified first by applying both methods to relevant processes that can be treated by both methods.     \r
-In this work, we have implemented and compared the applicability of several (?) classical potentials to ab initio results for one \r
-of the most important processes of our original question.   \r
-\r
-In the following we will present a comparative investigation of density functional theory (DFT) studies and \r
-classical potential calculations of the structure, energetics and mobility of carbon defects in silicon. \r
+Next to the fabrication of 3C-SiC layers by chemical vapor deposition (CVD) and molecular beam epitaxy (MBE) on hexagonal SiC\cite{powell90,fissel95,fissel95_apl} and Si\cite{nishino83,nishino87,kitabatake93,fissel95_apl} substrates, high-dose carbon implantation into crystalline silicon (c-Si) with subsequent or in situ annealing was found to result in SiC microcrystallites in Si\cite{borders71}.\r
+% maybe split CVD and MBE from IBS and explain remaining problems:\r
+% - on 6H-SiC: twin boundaries\r
+% - on Si: structural defects due to thermal conductivity and lattice mismatch\r
+Utilized and enhanced, ion beam synthesis (IBS) has become a promising method to form thin SiC layers of high quality exclusively of the 3C polytype embedded in and epitactically aligned to the Si host featuring a sharp interface\cite{lindner99,lindner01,lindner02}.\r
+% precipitation model\r
+However, only little is known on the SiC conversion in C implanted Si.\r
+High resolution transmission electron microscopy (HREM) studies\cite{werner96,werner97,lindner99_2} suggest the formation of C-Si dimers (dumbbells) on regular Si lattice sites, which agglomerate into large clusters indicated by dark contrasts and otherwise undisturbed Si lattice fringes in HREM.\r
+Once a critical radius of 2 nm to 4 nm is reached a topotactic transformation into a 3C-SiC precipitate occurs.\r
+The transformation is manifested by the disappearance of dark contrasts in favor of Moir\'e patterns due to the lattice mismatch of 20 \% of the 3C-SiC precipitate and c-Si.\r
+The insignificantly lower Si density of SiC ($\approx 4$ \%) compared to c-Si results in the emission of only a few excess Si atoms.\r
+% motivation to understand the precipitation and link to atomistic simulations\r
+A detailed understanding of the underlying processes will enable significant technological progress in 3C-SiC thin film formation and likewise offer perspectives for processes which rely upon prevention of precipitation events, e.g. the fabrication of strained pseudomorphic Si$_{1-y}$C$_y$ heterostructures\cite{strane96,laveant2002}.\r
+\r
+Atomistic simulations offer a powerful tool to study materials on a microscopic level providing detailed insight not accessible by experiment.\r
+Relevant structures consisting of $\approx 10^4$ atoms for the nanocrystal and even more atoms for a reasonably sized Si host matrix are too large to be completely described by high accuracy quantum mechanical methods.\r
+Directly modelling the dynamics of the processes mentioned above almost inevitably requires the atomic interaction to be described by less accurate though computationally more efficient classical potentials.\r
+The most common empirical potentials for covalent systems are the Stillinger-Weber\cite{stillinger85}, Brenner\cite{brenner90}, Tersoff\cite{tersoff_si3} and environment-dependent interatomic (EDIP)\cite{bazant96,bazant97,justo98} potential.\r
+From the mentioned potentials, until recently\cite{lucas10}, a parametrization to describe the C-Si multicomponent system did only exist for the Tersoff potential\cite{tersoff_m}.\r
+Description successful ... and failed ...\r
+Whether such potentials are appropriate for the description of the physical problem has, however, to be verified first by applying classical and quantum-mechanical methods to relevant processes that can be treated by both methods.\r
+In this work, the applicability of a Tersoff-like bond order potential\cite{albe_sic_pot} to some basic processes involved in the initially mentioned SiC precipitation mechanism is investigated by comparing results gained by classical and ab inito calculations.\r
+\r
+In the following a comparative investigation of density functional theory (DFT) studies and classical potential calculations of the structure, energetics and mobility of carbon defects in silicon is presented.\r
 \r
 %  --------------------------------------------------------------------------------\r
 \section{Methodology}\r